Scan set pruning for queries with predicates on semi-structured fields

ABSTRACT

A source table organized into a set of batch units is accessed. The source table comprises a column of data corresponding to a semi-structured data type. One or more indexing transformations for an object in the column are generated. The generating of the one or more indexing transformation includes converting the object to one or more stored data types. A pruning index is generated for the source table based in part on the one or more indexing transformations. The pruning index comprises a set of filters that index distinct values in each column of the source table, and each filter corresponds to a batch unit in the set of batch units. The pruning index is stored in a database with an association with the source table.

PRIORITY CLAIM

This application is a Continuation of U.S. patent application Ser. No.17/655,124, entitled, “PROCESSING QUERIES ON SEMI-STRUCTURED DATACOLUMNS,” filed Mar. 16, 2022, now issued as U.S. Pat. No. 11,494,384,which is a continuation of U.S. Pat. No. 11,308,090, entitled “PRUNINGINDEX TO SUPPORT SEMI-STRUCTURED DATA TYPES,” filed Aug. 4, 2021, whichclaims priority to U.S. Provisional Patent Application No. 63/197,750,entitled “PRUNING INDEX TO SUPPORT SEMI-STRUCTURED DATA TYPES,” filedJun. 7, 2021 and is also a continuation-in-part of U.S. Pat. No.11,308,089, entitled “PRUNING INDEX MAINTENANCE,” filed Jun. 25, 2021,which is a continuation of U.S. Pat. No. 11,086,875, entitled “DATABASEQUERY PROCESSING USING A PRUNING INDEX,” filed Jan. 28, 2021, which is acontinuation of U.S. Pat. No. 10,942,925, entitled “DATABASE QUERYPROCESSING USING A PRUNING INDEX,” filed on Jul. 17, 2020, which is acontinuation of U.S. Pat. No. 10,769,150, entitled “PRUNING INDEXES TOENHANCE DATABASE QUERY PROCESSING,” filed on Dec. 26, 2019, all of whichare incorporated herein by reference in their entireties.

TECHNICAL FIELD

Embodiments of the disclosure relate generally to databases and, morespecifically, to generating and using pruning indexes to optimizeprocessing of queries with semi-structured data types in a databasesystem.

BACKGROUND

When certain information is to be extracted from a database, a querystatement may be executed against the database data. A database systemprocesses the query and returns certain data according to one or moresearch conditions that indicate what information should be returned bythe query. The database system extracts specific data from the databaseand formats that data into a readable form. However, it can bechallenging to execute queries on a very large table because asignificant amount of time and computing resources are required to scanan entire table to identify data that satisfies the query.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the disclosure.

FIG. 1 illustrates an example computing environment that includes anetwork-based database system in communication with a cloud storageprovider system, in accordance with some embodiments of the presentdisclosure.

FIG. 2 is a block diagram illustrating components of a compute servicemanager, in accordance with some embodiments of the present disclosure.

FIG. 3 is a block diagram illustrating components of an executionplatform, in accordance with some embodiments of the present disclosure.

FIG. 4 is a conceptual diagram illustrating generation of an exampleblocked bloom filter, which may form part of a pruning index, inaccordance with some example embodiments.

FIG. 5 illustrates a portion of an example pruning index, in accordancewith some embodiments of the present disclosure.

FIG. 6 is a conceptual diagram illustrating further details regardingthe creation of an example pruning index, in accordance with someembodiments.

FIG. 7 is a conceptual diagram illustrating maintenance of a pruningindex, in accordance with some embodiments.

FIGS. 8-12 are flow diagrams illustrating operations of thenetwork-based database system in performing a method for generating andusing a pruning index in processing a database query, in accordance withsome embodiments of the present disclosure.

FIG. 13 illustrates a diagrammatic representation of a machine in theform of a computer system within which a set of instructions may beexecuted for causing the machine to perform any one or more of themethodologies discussed herein, in accordance with some embodiments ofthe present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to specific example embodiments forcarrying out the inventive subject matter. Examples of these specificembodiments are illustrated in the accompanying drawings, and specificdetails are set forth in the following description in order to provide athorough understanding of the subject matter. It will be understood thatthese examples are not intended to limit the scope of the claims to theillustrated embodiments. On the contrary, they are intended to coversuch alternatives, modifications, and equivalents as may be includedwithin the scope of the disclosure.

As noted above, processing queries directed to very large tables ischallenging because a significant amount of time and computing resourcesare required to scan an entire table to identify data that satisfies thequery. Therefore, it can be desirable to execute a query withoutscanning the entire table. Aspects of the present disclosure address theabove and other challenges in processing queries on large tables bycreating a pruning index that may be used to construct a reduced scanset for processing a query. More specifically, a large source table maybe organized into a set of batch units such as micro-partitions, and apruning index can be created for the source table to be used inidentifying a subset of the batch units to scan to identify data thatsatisfies the query.

It is common for data to be stored by database systems insemi-structured formats, which can store objects of any kind such asnumbers, strings, timestamps, or the like. Accordingly, the pruningindexes described herein are configured to support primitive data types(e.g., STRING, NUMBER, or the like) as well as such semi-structured andcomplex (e.g., ARRAY and OBJECT) data types.

Consistent with some embodiments, a network-based database systemgenerates a pruning index for a source table and uses the pruning indexto prune micro-partitions of the source table when processing queriesdirected to the source table. The pruning index includes a probabilisticdata structure that stores fingerprints for all searchable values in asource table. The fingerprints are based on hashes computed based onsearchable values in the source table. To support semi-structured datatype values, hashes can be computed over indexing transformations ofsearchable values. That is, for each semi-structured data type value,one or more indexing transformations are generated and the fingerprintsare generated based on hashes computed over the one or more indexingtransformations. An indexing transformation is generated by converting asemi-structured data value to a primitive data type. Semi-structureddata types are automatically parsed to identify all paths that can beindexed. To support partial matching queries, fingerprints can begenerated by computing a hash over a set of N-grams generated based on asearchable value, in some embodiments.

In generating a pruning index, the network-based database system usesthe fingerprints to generate a filter for each micro-partition of thesource table that indexes distinct values (or distinct N-grams ofsearchable values) in each column of the micro-partition of the sourcetable. The filter may, for example, comprise a blocked bloom filter, abloom filter, a hash filter, or a cuckoo filter.

For a given query, the pruning index can be used to quickly disqualifymicro-partitions that are certain to not include data that satisfies thequery. When a query is received, rather than scanning the entire sourcetable to identify matching data, the network-based database systemprobes the pruning index to identify a reduced scan set ofmicro-partitions comprising only a subset of the micro-partitions of thesource table, and only the reduced scan set of micro-partitions isscanned when executing the query.

The database system can use a pruning index to prune a scan set forqueries with equality predicates (e.g., “=”) and queries with patternmatching predicates (e.g., LIKE, ILIKE, CONTAINS, STARTSWITH, ENDSWITH,etc.) on both structured and semi-structured data types. As discussedherein, a “predicate” comprises an expression (e.g., a SQL expression)that evaluates a search condition that is either TRUE, FALSE, orUNKNOWN. For a given equality predicate, the database system uses thepruning index to identify a subset of micro-partitions to scan for datathat matches an entire string or other searchable value. For a givenpattern matching predicate, the database system uses the pruning indexto identify a set of micro-partitions to scan for data that matches aspecified search pattern, which can include one or more partial stringsand one or more wildcards (e.g., “%” or “_”) used to represent wildcardcharacter positions in the pattern (e.g., character positions whoseunderlying value is unconstrained by the query).

By using a pruning index to prune the set of micro-partitions to scan inexecuting a query, the database system accelerates the execution ofpoint queries on large tables when compared to conventionalmethodologies. Using a pruning index in this manner also guarantees aconstant overhead for every searchable value on the table. Additionalbenefits of pruning index utilization include, but are not limited to,an ability to support multiple predicate types, an ability to quicklycompute the number of distinct values in a table, and the ability tosupport join pruning.

In addition, by utilizing indexing transformations when building thepruning index, query predicates on semi-structured fields can besupported. Contrary to conventional approaches, this approach does notrequire manual selection of semi-structured data fields to be indexed.Further, unlike conventional approaches, this approach does not use anyadditional storage or concepts such as virtual columns or generatedcolumns to store the fields to be indexed. Also, the pruning indexesdescribed herein support indexing and matching against predicatesregardless of how nested or evolving the structure of the input data is.Moreover, this approach does not enforce any data type restrictions onthe semi-structured data fields and the values in the predicate.Finally, the generation of the pruning index involves cast-sensitiveindexing of individual semi-structured data type fields, meaning thateach input record can be attempted to be converted to relevant datatypes to match with casting behavior of semi-structured data typecolumns.

As discussed herein, a “micro-partition” is a batch unit, and eachmicro-partition has contiguous units of storage. By way of example, eachmicro-partition may contain between 50 MB and 500 MB of uncompresseddata (note that the actual size in storage may be smaller because datamay be stored compressed). Groups of rows in tables may be mapped intoindividual micro-partitions organized in a columnar fashion. This sizeand structure allow for extremely granular selection of themicro-partitions to be scanned, which can comprise millions, or evenhundreds of millions, of micro-partitions. This granular selectionprocess for micro-partitions to be scanned is referred to herein as“pruning.” Pruning involves using metadata to determine which portionsof a table, including which micro-partitions or micro-partitiongroupings in the table, are not pertinent to a query, and then avoidingthose non-pertinent micro-partitions when responding to the query andscanning only the pertinent micro-partitions to respond to the query.Metadata may be automatically gathered about all rows stored in amicro-partition, including: the range of values for each of the columnsin the micro-partition; the number of distinct values; and/or additionalproperties used for both optimization and efficient query processing. Inone embodiment, micro-partitioning may be automatically performed on alltables. For example, tables may be transparently partitioned using theordering that occurs when the data is inserted/loaded. However, itshould be appreciated that this disclosure of the micro-partition isexemplary only and should be considered non-limiting. It should beappreciated that the micro-partition may include other database storagedevices without departing from the scope of the disclosure.

FIG. 1 illustrates an example computing environment 100 that includes adatabase system 102 in communication with a storage platform 104, inaccordance with some embodiments of the present disclosure. To avoidobscuring the inventive subject matter with unnecessary detail, variousfunctional components that are not germane to conveying an understandingof the inventive subject matter have been omitted from FIG. 1 . However,a skilled artisan will readily recognize that various additionalfunctional components may be included as part of the computingenvironment 100 to facilitate additional functionality that is notspecifically described herein.

As shown, the computing environment 100 comprises the database system102 and a storage platform 104 (e.g., AWS®, Microsoft Azure BlobStorage®, or Google Cloud Storage®). The database system 102 is used forreporting and analysis of integrated data from one or more disparatesources including storage devices 106-1 to 106-N within the storageplatform 104. The storage platform 104 comprises a plurality ofcomputing machines and provides on-demand computer system resources suchas data storage and computing power to the database system 102.

The database system 102 comprises a compute service manager 108, anexecution platform 110, and a database 114. The database system 102hosts and provides data reporting and analysis services to multipleclient accounts. Administrative users can create and manage identities(e.g., users, roles, and groups) and use permissions to allow or denyaccess to the identities to resources and services.

The compute service manager 108 coordinates and manages operations ofthe database system 102. The compute service manager 108 also performsquery optimization and compilation as well as managing clusters ofcompute services that provide compute resources (also referred to as“virtual warehouses”). The compute service manager 108 can support anynumber of client accounts such as end users providing data storage andretrieval requests, system administrators managing the systems andmethods described herein, and other components/devices that interactwith compute service manager 108.

The compute service manager 108 is also in communication with a userdevice 112. The user device 112 corresponds to a user of one of themultiple client accounts supported by the database system 102. In someembodiments, the compute service manager 108 does not receive any directcommunications from the user device 112 and only receives communicationsconcerning jobs from a queue within the database system 102.

The compute service manager 108 is also coupled to database 114, whichis associated with the data stored in the computing environment 100. Thedatabase 114 stores data pertaining to various functions and aspectsassociated with the database system 102 and its users. In someembodiments, the database 114 includes a summary of data stored inremote data storage systems as well as data available from a localcache. Additionally, the database 114 may include information regardinghow data is organized in remote data storage systems (e.g., the storageplatform 104) and the local caches. The database 114 allows systems andservices to determine whether a piece of data needs to be accessedwithout loading or accessing the actual data from a storage device.

For example, the database 114 can include one or more pruning indexes.The compute service manager 108 may generate a pruning index for eachsource table accessed from the storage platform 104 and use a pruningindex to prune the set of micro-partitions of a source table to scan fordata in executing a query. That is, given a query directed at a sourcetable organized into a set of micro-partitions, the compute servicemanager 108 can access a pruning index from the database 114 and use thepruning index to identify a reduced set of micro-partitions to scan inexecuting the query. The set of micro-partitions to scan in executing aquery may be referred to herein as a “scan set.”

In some embodiments, the compute service manager 108 may determine thata job should be performed based on data from the database 114. In suchembodiments, the compute service manager 108 may scan the data anddetermine that a job should be performed to improve data organization ordatabase performance. For example, the compute service manager 108 maydetermine that a new version of a source table has been generated andthe pruning index has not been refreshed to reflect the new version ofthe source table. The database 114 may include a transactional changetracking stream indicating when the new version of the source table wasgenerated and when the pruning index was last refreshed. Based on thattransaction stream, the compute service manager 108 may determine that ajob should be performed. In some embodiments, the compute servicemanager 108 determines that a job should be performed based on a triggerevent and stores the job in a queue until the compute service manager108 is ready to schedule and manage the execution of the job. In anembodiment of the disclosure, the compute service manager 108 determineswhether a table or pruning index needs to be reclustered based on one ormore DML commands being performed, wherein one or more of the DMLcommands constitute the trigger event.

The compute service manager 108 is further coupled to the executionplatform 110, which provides multiple computing resources that executevarious data storage and data retrieval tasks. The execution platform110 is coupled to storage platform 104 of the storage platform 104. Thestorage platform 104 comprises multiple data storage devices 106-1 to106-N. In some embodiments, the data storage devices 106-1 to 106-N arecloud-based storage devices located in one or more geographic locations.For example, the data storage devices 106-1 to 106-N may be part of apublic cloud infrastructure or a private cloud infrastructure. The datastorage devices 106-1 to 106-N may be hard disk drives (HDDs), solidstate drives (SSDs), storage clusters, Amazon S3™ storage systems or anyother data storage technology. Additionally, the storage platform 104may include distributed file systems (e.g., Hadoop Distributed FileSystems (HDFS)), object storage systems, and the like.

The execution platform 110 comprises a plurality of compute nodes. A setof processes on a compute node executes a query plan compiled by thecompute service manager 108. The set of processes can include: a firstprocess to execute the query plan; a second process to monitor anddelete micro-partition files using a least recently used (LRU) policyand implement an out of memory (OOM) error mitigation process; a thirdprocess that extracts health information from process logs and status tosend back to the compute service manager 108; a fourth process toestablish communication with the compute service manager 108 after asystem boot; and a fifth process to handle all communication with acompute cluster for a given job provided by the compute service manager108 and to communicate information back to the compute service manager108 and other compute nodes of the execution platform 110.

In some embodiments, communication links between elements of thecomputing environment 100 are implemented via one or more datacommunication networks. These data communication networks may utilizeany communication protocol and any type of communication medium. In someembodiments, the data communication networks are a combination of two ormore data communication networks (or sub-networks) coupled to oneanother. In alternate embodiments, these communication links areimplemented using any type of communication medium and any communicationprotocol.

As shown in FIG. 1 , the data storage devices 106-1 to 106-N aredecoupled from the computing resources associated with the executionplatform 110. This architecture supports dynamic changes to the databasesystem 102 based on the changing data storage/retrieval needs as well asthe changing needs of the users and systems. The support of dynamicchanges allows the database system 102 to scale quickly in response tochanging demands on the systems and components within the databasesystem 102. The decoupling of the computing resources from the datastorage devices supports the storage of large amounts of data withoutrequiring a corresponding large amount of computing resources.Similarly, this decoupling of resources supports a significant increasein the computing resources utilized at a particular time withoutrequiring a corresponding increase in the available data storageresources.

The compute service manager 108, database 114, execution platform 110,and storage platform 104 are shown in FIG. 1 as individual discretecomponents. However, each of the compute service manager 108, database114, execution platform 110, and storage platform 104 may be implementedas a distributed system (e.g., distributed across multiplesystems/platforms at multiple geographic locations). Additionally, eachof the compute service manager 108, database 114, execution platform110, and storage platform 104 can be scaled up or down (independently ofone another) depending on changes to the requests received and thechanging needs of the database system 102. Thus, in the describedembodiments, the database system 102 is dynamic and supports regularchanges to meet the current data processing needs.

During typical operation, the database system 102 processes multiplejobs determined by the compute service manager 108. These jobs arescheduled and managed by the compute service manager 108 to determinewhen and how to execute the job. For example, the compute servicemanager 108 may divide the job into multiple discrete tasks and maydetermine what data is needed to execute each of the multiple discretetasks. The compute service manager 108 may assign each of the multiplediscrete tasks to one or more nodes of the execution platform 110 toprocess the task. The compute service manager 108 may determine whatdata is needed to process a task and further determine which nodeswithin the execution platform 110 are best suited to process the task.Some nodes may have already cached the data needed to process the taskand, therefore, be a good candidate for processing the task. Metadatastored in the database 114 assists the compute service manager 108 indetermining which nodes in the execution platform 110 have alreadycached at least a portion of the data needed to process the task. One ormore nodes in the execution platform 110 process the task using datacached by the nodes and, if necessary, data retrieved from the storageplatform 104. It is desirable to retrieve as much data as possible fromcaches within the execution platform 110 because the retrieval speed istypically much faster than retrieving data from the storage platform104.

As shown in FIG. 1 , the computing environment 100 separates theexecution platform 110 from the storage platform 104. In thisarrangement, the processing resources and cache resources in theexecution platform 110 operate independently of the data storage devices106-1 to 106-N in the storage platform 104. Thus, the computingresources and cache resources are not restricted to specific datastorage devices 106-1 to 106-N. Instead, all computing resources and allcache resources may retrieve data from, and store data to, any of thedata storage resources in the storage platform 104.

FIG. 2 is a block diagram illustrating components of the compute servicemanager 108, in accordance with some embodiments of the presentdisclosure. As shown in FIG. 2 , the compute service manager 108includes an access manager 202 and a key manager 204 coupled to a datastorage device 206. Access manager 202 handles authentication andauthorization tasks for the systems described herein. Key manager 204manages storage and authentication of keys used during authenticationand authorization tasks. For example, access manager 202 and key manager204 manage the keys used to access data stored in remote storage devices(e.g., data storage devices in storage platform 104). As used herein,the remote storage devices may also be referred to as “persistentstorage devices” or “shared storage devices.”

A request processing service 208 manages received data storage requestsand data retrieval requests (e.g., jobs to be performed on databasedata). For example, the request processing service 208 may determine thedata necessary to process a received query (e.g., a data storage requestor data retrieval request). The data may be stored in a cache within theexecution platform 110 or in a data storage device in storage platform104.

A management console service 210 supports access to various systems andprocesses by administrators and other system managers. Additionally, themanagement console service 210 may receive a request to execute a joband monitor the workload on the system.

The compute service manager 108 also includes a job compiler 212, a joboptimizer 214 and a job executor 216. The job compiler 212 parses a jobinto multiple discrete tasks and generates the execution code for eachof the multiple discrete tasks. The job optimizer 214 determines thebest method to execute the multiple discrete tasks based on the datathat needs to be processed. The job optimizer 214 also handles variousdata pruning operations and other data optimization techniques toimprove the speed and efficiency of executing the job. The job executor216 executes the execution code for jobs received from a queue ordetermined by the compute service manager 108.

A job scheduler and coordinator 218 sends received jobs to theappropriate services or systems for compilation, optimization, anddispatch to the execution platform 110. For example, jobs may beprioritized and processed in that prioritized order. In an embodiment,the job scheduler and coordinator 218 determines a priority for internaljobs that are scheduled by the compute service manager 108 with other“outside” jobs such as user queries that may be scheduled by othersystems in the database but may utilize the same processing resources inthe execution platform 110. In some embodiments, the job scheduler andcoordinator 218 identifies or assigns particular nodes in the executionplatform 110 to process particular tasks. A virtual warehouse manager220 manages the operation of multiple virtual warehouses implemented inthe execution platform 110. As discussed below, each virtual warehouseincludes multiple execution nodes that each include a cache and aprocessor.

Additionally, the compute service manager 108 includes a configurationand metadata manager 222, which manages the information related to thedata stored in the remote data storage devices and in the local caches(e.g., the caches in execution platform 110). The configuration andmetadata manager 222 uses the metadata to determine which datamicro-partitions need to be accessed to retrieve data for processing aparticular task or job. A monitor and workload analyzer 224 overseesprocesses performed by the compute service manager 108 and manages thedistribution of tasks (e.g., workload) across the virtual warehouses andexecution nodes in the execution platform 110. The monitor and workloadanalyzer 224 also redistributes tasks, as needed, based on changingworkloads throughout the database system 102 and may furtherredistribute tasks based on a user (e.g., “external”) query workloadthat may also be processed by the execution platform 110. Theconfiguration and metadata manager 222 and the monitor and workloadanalyzer 224 are coupled to a data storage device 226. Data storagedevice 226 in FIG. 2 represents any data storage device within thedatabase system 102. For example, data storage device 226 may representcaches in execution platform 110, storage devices in storage platform104, or any other storage device.

As shown, the compute service manager 108 further includes a pruningindex generator 228. The pruning index generator 228 is responsible forgenerating pruning indexes to be used in pruning scan sets for queriesdirected to tables stored in the storage platform 104. Each pruningindex comprises a set of filters (e.g., blocked bloom filters, bloomfilters, hash filter, or cuckoo filters) that encode an existence ofunique values in each column of a source table. The pruning indexgenerator 228 generates a filter for each micro-partition of a sourcetable and each filter indicates whether data matching a query ispotentially stored on a particular micro-partition of the source table.Further details regarding the generation of pruning indexes arediscussed below.

FIG. 3 is a block diagram illustrating components of the executionplatform 110, in accordance with some embodiments of the presentdisclosure. As shown in FIG. 3 , the execution platform 110 includesmultiple virtual warehouses, including virtual warehouse 1, virtualwarehouse 2, and virtual warehouse n. Each virtual warehouse includesmultiple execution nodes that each includes a data cache and aprocessor. The virtual warehouses can execute multiple tasks in parallelby using the multiple execution nodes. As discussed herein, theexecution platform 110 can add new virtual warehouses and drop existingvirtual warehouses in real-time based on the current processing needs ofthe systems and users. This flexibility allows the execution platform110 to quickly deploy large amounts of computing resources when neededwithout being forced to continue paying for those computing resourceswhen they are no longer needed. All virtual warehouses can access datafrom any data storage device (e.g., any storage device in storageplatform 104).

Although each virtual warehouse shown in FIG. 3 includes three executionnodes, a particular virtual warehouse may include any number ofexecution nodes. Further, the number of execution nodes in a virtualwarehouse is dynamic, such that new execution nodes are created whenadditional demand is present, and existing execution nodes are deletedwhen they are no longer necessary.

Each virtual warehouse is capable of accessing any of the data storagedevices 106-1 to 106-N shown in FIG. 1 . Thus, the virtual warehousesare not necessarily assigned to a specific data storage device 106-1 to106-N and, instead, can access data from any of the data storage devices106-1 to 106-N within the storage platform 104. Similarly, each of theexecution nodes shown in FIG. 3 can access data from any of the datastorage devices 106-1 to 106-N. In some embodiments, a particularvirtual warehouse or a particular execution node may be temporarilyassigned to a specific data storage device, but the virtual warehouse orexecution node may later access data from any other data storage device.

In the example of FIG. 3 , virtual warehouse 1 includes three executionnodes 302-1, 302-2, and 302-N. Execution node 302-1 includes a cache304-1 and a processor 306-1. Execution node 302-2 includes a cache 304-2and a processor 306-2. Execution node 302-N includes a cache 304-N and aprocessor 306-N. Each execution node 302-1, 302-2, and 302-N isassociated with processing one or more data storage and/or dataretrieval tasks. For example, a virtual warehouse may handle datastorage and data retrieval tasks associated with an internal service,such as a clustering service, a materialized view refresh service, afile compaction service, a storage procedure service, or a file upgradeservice. In other implementations, a particular virtual warehouse mayhandle data storage and data retrieval tasks associated with aparticular data storage system or a particular category of data.

Similar to virtual warehouse 1 discussed above, virtual warehouse 2includes three execution nodes 312-1, 312-2, and 312-N. Execution node312-1 includes a cache 314-1 and a processor 316-1. Execution node 312-2includes a cache 314-2 and a processor 316-2. Execution node 312-Nincludes a cache 314-N and a processor 316-N. Additionally, virtualwarehouse N includes three execution nodes 322-1, 322-2, and 322-N.Execution node 322-1 includes a cache 324-1 and a processor 326-1.Execution node 322-2 includes a cache 324-2 and a processor 326-2.Execution node 322-N includes a cache 324-N and a processor 326-N.

In some embodiments, the execution nodes shown in FIG. 3 are statelesswith respect to the data the execution nodes are caching. For example,these execution nodes do not store or otherwise maintain stateinformation about the execution node or the data being cached by aparticular execution node. Thus, in the event of an execution nodefailure, the failed node can be transparently replaced by another node.Since there is no state information associated with the failed executionnode, the new (replacement) execution node can easily replace the failednode without concern for recreating a particular state.

Although the execution nodes shown in FIG. 3 each includes one datacache and one processor, alternate embodiments may include executionnodes containing any number of processors and any number of caches.Additionally, the caches may vary in size among the different executionnodes. The caches shown in FIG. 3 store, in the local execution node,data that was retrieved from one or more data storage devices in storageplatform 104. Thus, the caches reduce or eliminate the bottleneckproblems occurring in platforms that consistently retrieve data fromremote storage systems. Instead of repeatedly accessing data from theremote storage devices, the systems and methods described herein accessdata from the caches in the execution nodes, which is significantlyfaster and avoids the bottleneck problem discussed above. In someembodiments, the caches are implemented using high-speed memory devicesthat provide fast access to the cached data. Each cache can store datafrom any of the storage devices in the storage platform 104.

Further, the cache resources and computing resources may vary betweendifferent execution nodes. For example, one execution node may containsignificant computing resources and minimal cache resources, making theexecution node useful for tasks that require significant computingresources. Another execution node may contain significant cacheresources and minimal computing resources, making this execution nodeuseful for tasks that require caching of large amounts of data. Yetanother execution node may contain cache resources providing fasterinput-output operations, useful for tasks that require fast scanning oflarge amounts of data. In some embodiments, the cache resources andcomputing resources associated with a particular execution node aredetermined when the execution node is created, based on the expectedtasks to be performed by the execution node.

Additionally, the cache resources and computing resources associatedwith a particular execution node may change over time based on changingtasks performed by the execution node. For example, an execution nodemay be assigned more processing resources if the tasks performed by theexecution node become more processor-intensive. Similarly, an executionnode may be assigned more cache resources if the tasks performed by theexecution node require a larger cache capacity.

Although virtual warehouses 1, 2, and n are associated with the sameexecution platform 110, the virtual warehouses may be implemented usingmultiple computing systems at multiple geographic locations. Forexample, virtual warehouse 1 can be implemented by a computing system ata first geographic location, while virtual warehouses 2 and n areimplemented by another computing system at a second geographic location.In some embodiments, these different computing systems are cloud-basedcomputing systems maintained by one or more different entities.

Additionally, each virtual warehouse is shown in FIG. 3 as havingmultiple execution nodes. The multiple execution nodes associated witheach virtual warehouse may be implemented using multiple computingsystems at multiple geographic locations. For example, an instance ofvirtual warehouse 1 implements execution nodes 302-1 and 302-2 on onecomputing platform at a geographic location and implements executionnode 302-N at a different computing platform at another geographiclocation. Selecting particular computing systems to implement anexecution node may depend on various factors, such as the level ofresources needed for a particular execution node (e.g., processingresource requirements and cache requirements), the resources availableat particular computing systems, communication capabilities of networkswithin a geographic location or between geographic locations, and whichcomputing systems are already implementing other execution nodes in thevirtual warehouse.

Execution platform 110 is also fault tolerant. For example, if onevirtual warehouse fails, that virtual warehouse is quickly replaced witha different virtual warehouse at a different geographic location.

A particular execution platform 110 may include any number of virtualwarehouses. Additionally, the number of virtual warehouses in aparticular execution platform is dynamic, such that new virtualwarehouses are created when additional processing and/or cachingresources are needed. Similarly, existing virtual warehouses may bedeleted when the resources associated with the virtual warehouse are nolonger necessary.

In some embodiments, the virtual warehouses may operate on the same datain storage platform 104, but each virtual warehouse has its ownexecution nodes with independent processing and caching resources. Thisconfiguration allows requests on different virtual warehouses to beprocessed independently and with no interference between the requests.This independent processing, combined with the ability to dynamicallyadd and remove virtual warehouses, supports the addition of newprocessing capacity for new users without impacting the performanceobserved by the existing users.

FIG. 4 is a conceptual diagram illustrating generation of a filter 400,which forms part of a pruning index generated by the database system 102based on a source table 402, in accordance with some exampleembodiments. As shown, the source table 402 is organized into multiplemicro-partitions and each micro-partition comprises multiple columns inwhich values are stored.

In generating a pruning index, the compute service manager 108 generatesa filter for each micro-partition of the source table 402, an example ofwhich is illustrated in FIG. 4 as blocked bloom filter 400. Blockedbloom filter 400 comprises multiple bloom filters and encodes theexistence of distinct values present in each column of the correspondingmicro-partition. When a query is received, rather than scanning theentire source table 402 to evaluate the query, the database system 102probes the pruning index to identify a reduced scan set ofmicro-partitions comprising only a subset of the micro-partitions of thesource table 402.

As shown, the blocked bloom filter 400 is decomposed into N bloomfilters stored as individual columns of the pruning index to leveragecolumnar scans. In generating the blocked bloom filter 400 for aparticular micro-partition of the source table 402, values of storedvalues or preprocessed variants thereof are transformed into bitpositions in the bloom filters. For example, a set of fingerprints(e.g., hash values) can be generated from stored values (or N-gramsgenerated from stored values) in each column of the micro-partition andthe set of fingerprints may be used to set bits in the bloom filters.Each line of the blocked bloom filter 400 is encoded and stored as asingle row in the pruning index. Each bloom filter 400 is represented inthe pruning index as a two-dimensional array indexed by the fingerprintsfor the stored column values.

FIG. 5 illustrates a portion of an example pruning index 500, inaccordance with some embodiments of the present disclosure. The examplepruning index 500 is organized into a plurality of rows and columns. Thecolumns of the pruning index 500 comprise a partition number 502 tostore a partition identifier and a blocked bloom filter 504 (e.g., theblocked bloom filter 400) that is decomposed into multiple numericcolumns; each column in the blocked bloom filter 504 represents a bloomfilter. To avoid obscuring the inventive subject matter with unnecessarydetail, various additional columns that are not germane to conveying anunderstanding of the inventive subject matter may have been omitted fromthe example pruning index 500 in FIG. 5 .

FIG. 6 is a conceptual diagram illustrating creation of an examplepruning index, in accordance with some embodiments. The creation of afilter (e.g., a blocked bloom filter) is performed by a specializedoperator within the compute service manager 108 that computes the set ofrows of the pruning index. This operator obtains all the columns of aparticular micro-partition of a source table and populates the filterfor that micro-partition.

If the total number of distinct values (or distinct N-grams of storedvalues) in the source table is unknown, the compute service manager 108allocates a maximum number of levels to the pruning index, populateseach filter, and then applies a consolidation phase to merge thedifferent filters in a final representation of the pruning index. Thememory allocated to compute this information per micro-partition isconstant. In the example illustrated in FIG. 6 , the memory allocated tocompute this information is a two-dimensional array of unsignedintegers. The first dimension is indexed by the level (maximum number oflevels) and the second dimension is indexed by the number of bloomfilters. Since each partition is processed by a single thread, the totalmemory is bounded by the number of threads (e.g., 8) and the maximumlevel of levels.

As shown in FIG. 6 , at each partition boundary, the compute servicemanager 108 combines blocks based on a target bloom filter density. Forexample, the compute service manager 108 may combine blocks such thatthe bloom filter density is no more than half. Since the domain offingerprints (e.g., hashed values) is uniform, this can be doneincrementally or globally based on the observed number of distinctvalues computed above.

If the number of distinct values is known, the compute service manager108 determines the number of levels for the pruning index by dividingthe maximum number of distinct values (or distinct N-grams) by thenumber of distinct values (or distinct N-grams) per level. To combinetwo levels, the compute service manager 108 performs a logical OR on allthe integers representing the filter.

For performance reasons, the filter functions (create and check) cancombine two hash functions (e.g., two 32-bit hash functions). Both thehash function computation and the filter derivation need to be identicalon both the execution platform 110 and compute service manager 108 toallow for pruning in compute service manager 108 and in the scan setinitialization in the execution platform 110.

FIG. 7 is a conceptual diagram illustrating maintenance of a pruningindex based on changes to a source table, in accordance with someembodiments. As shown, at 700, a change is made to a source table (e.g.,addition of one or more rows or columns). The change to the source tabletriggers generation of additional rows in the pruning index for eachchanged or new micro-partition of the source table, at 702. At a regularinterval, the newly produced rows in the pruning index are reclustered,at 704.

The compute service manager 108 uses a deterministic selection algorithmas part of clustering the prune index. The processing of eachmicro-partition in the source table creates a bounded (and mostlyconstant) number of rows based on the number of distinct values (orN-grams of stored values) in the source micro-partition. Byconstruction, those rows are known to be unique and the index domain isnon-overlapping for that partition and fully overlapping with alreadyclustered index rows. To minimize the cost of clustering, the computeservice manager 108 delays reclustering of rows until a threshold numberof rows have been produced to create constant partitions.

Although the pruning index is described in some embodiments as beingimplemented specifically with blocked bloom filters, it shall beappreciated that the pruning index is not limited to blocked bloomfilters, and in other embodiments, the pruning index may be implementedusing other filters such as bloom filters, hash filters, or cuckoofilters.

FIGS. 8-12 are flow diagrams illustrating operations of the databasesystem 102 in performing a method 800 for generating and using a pruningindex in processing a database query, in accordance with someembodiments of the present disclosure. The method 800 may be embodied incomputer-readable instructions for execution by one or more hardwarecomponents (e.g., one or more processors) such that the operations ofthe method 800 may be performed by components of database system 102.Accordingly, the method 800 is described below, by way of example withreference thereto. However, it shall be appreciated that method 800 maybe deployed on various other hardware configurations and is not intendedto be limited to deployment within the database system 102.

Depending on the embodiment, an operation of the method 800 may berepeated in different ways or involve intervening operations not shown.Though the operations of the method 800 may be depicted and described ina certain order, the order in which the operations are performed mayvary among embodiments, including performing certain operations inparallel or performing sets of operations in separate processes. Forexample, although the use and generation of the pruning index aredescribed and illustrated together as part of the method 800, it shallbe appreciated that the use and generation of the pruning index may beperformed as separate processes, consistent with some embodiments.

At operation 805, the compute service manager 108 accesses a sourcetable that is organized into a plurality of micro-partitions. The sourcetable comprises a plurality of cells organized into rows and columns anda data value is included in each cell.

At operation 810, the compute service manager 108 generates a pruningindex based on the source table. The pruning index comprises a set offilters (e.g., a set of blocked bloom filters) that index distinctvalues (or distinct N-grams of stored values) in each column of eachmicro-partition of the source table. A filter is generated for eachmicro-partition in the source table and each filter is decomposed intomultiple numeric columns (e.g., 32 numeric columns) to enable integercomparisons. Consistent with some embodiments, the pruning indexcomprises a plurality of rows and each row comprises at least amicro-partition identifier and a set of bloom filters. Consistent withsome embodiments, the compute service manager 108 generates the pruningindex in an offline process before receiving a query.

At operation 815, the compute service manager 108 receives a querydirected at the source table. The query can comprise an equalitypredicate (e.g., “=”) or a pattern matching predicate (e.g., LIKE,ILIKE, CONTAINS, STARTSWITH, or ENDSWITH). In instances in which thequery includes a pattern matching predicate, the query specifies asearch pattern for which matching stored data in the source table is tobe identified. A query predicate can be directed to primitive data types(e.g., STRING, NUMBER, or the like), complex data types (e.g., ARRAY orOBJECT), semi-structured data types (e.g., JSON, XML, Parquet, and ORC),or combinations thereof.

At operation 820, the compute service manager 108 accesses the pruningindex associated with the source table based on the query being directedat the source table. For example, the database 114 may store informationdescribing associations between tables and pruning indexes.

At operation 825, the compute service manager 108 uses the pruning indexto prune the set of micro-partitions of the source table to be scannedfor data that satisfies the query (e.g., a data value that satisfies theequality predicate or data that matches the search pattern). That is,the compute service manager 108 uses the pruning index to identify areduced scan set comprising only a subset of the micro-partitions of thesource table. The reduced scan set includes one or more micro-partitionsin which data that satisfies the query is potentially stored. The subsetof micro-partitions of the source table include micro-partitionsdetermined to potentially include data that satisfies the query based onthe set of bloom filters in the pruning index.

At operation 830, the execution platform 110 processes the query. Inprocessing the query, the execution platform 110 scans the subset ofmicro-partitions of the reduced scan set while foregoing a scan of theremaining micro-partitions. In this way, the execution platform 110searches only micro-partitions where matching data is potentially storedwhile foregoing an expenditure of additional time and resources to alsosearch the remaining micro-partitions for which it is known, based onthe pruning index, that matching data is not stored.

Consistent with some embodiments, rather than providing a reduced scanset with micro-partitions of the source table to scan for data, thecompute service manager 108 may instead identify and compile a set ofnon-matching micro-partitions. The compute service manager 108 or theexecution platform 110 may remove micro-partitions from the scan setbased on the set of non-matching micro-partitions.

As shown in FIG. 9 , the method 800 may, in some embodiments, furtherinclude operations 905 and 910. Consistent with these embodiments, theoperations 905 and 910 may be performed as part of the operation 810where the compute service manager 108 generates the pruning index. Theoperations 905 and 910 are described below in reference to a singlemicro-partition of the source table simply for ease of explanation.However, it shall be appreciated that in generating the pruning index,the compute service manager 108 generates a filter for eachmicro-partition of the source table, and thus the operations 905 and 910may be performed for each micro-partition of the source table.

At operation 905, the compute service manager 108 generates a filter fora micro-partition of the source table. For example, the compute servicemanager 108 may generate a blocked bloom filter for the micro-partitionthat indexes distinct values (or distinct N-grams of values) in eachcolumn of the micro-partition of the source table. The generating of thefilter can include generating a set of fingerprints for each searchabledata value in the micro-partition.

Given that objects in semi-structured data type columns can be stored aspotentially multiple different data types by the network-based databasesystem 102 (referred to herein as “stored data types”), the computeservice manager 108 can, in some embodiments, generate fingerprints fora given object in a semi-structured column of the source table based onone or more data type transformations generated for the object, as willbe discussed in further detail below. A data type transformation can begenerated by converting a data object into a stored data type, forexample, using an SQL Cast Function (also referred to simply as a“cast”). By generating fingerprints in this matter, the compute servicemanager 108 can support indexing of semi-structured data type objectsincluded in the source table.

In some embodiments, for a given data value in the micro-partition, thecompute service manager 108 can generate the set of fingerprints basedon a set of N-grams generated for the data value. The set of N-grams canbe generated based on the data value or one or more preprocessedvariants of the data value. The compute service manager 108 can generatea fingerprint based on a hash that is computed of an N-gram.

In computing the hash, the compute service manager 108 may utilize arolling hash function or other known hashing scheme that allowsindividual characters to be added or removed from a window ofcharacters. An example hash function used by the compute service manager108 is the XxHash( ) function, although other known hash functions canbe utilized. Each generated fingerprint is used to populate a cell inthe filter.

At operation 910, which is optional in some embodiments, the computeservice manager 108 merges one or more rows of the filter. The computeservice manager 108 can merge rows by performing a logical OR operation.The compute service manager 108 may merge rows of the filter until adensity threshold is reached, where the density refers to the ratio of1's and 0's in a row. The density threshold may be based on a targetfalse positive rate.

The source table can include one or more columns of data of asemi-structured data type used to store objects of any kind such asprimitive data types like numbers, strings, binary data, date, time, andtimestamp values, as well as compound data types such as objects andarrays that store a nested structure inside. Accordingly, it isimportant that pruning indexes generated by the database system 102 alsosupport query predicates on semi-structured data types in addition topredicates on primitive data-type fields. As non-limiting examples, apruning index can be generated to support the following types ofpredicates:

-   -   . . . where        <path_to_semi-structured_data_type_field>=<constant>;    -   . . . where        <path_to_semi-structured_data_type_field>::<cast_to_type>=<constant>    -   . . . where <semi-structured_data_type_column>=<constant>;    -   . . . where        <path_to_semi-structured_data_type_field>like‘%pattern%’;    -   . . . where <semi-structured_data_type_column>like‘%pattern%’;    -   . . . where array_contains(<value>, <array>);    -   . . . where arrays_overlap(<array1>, <array2>)    -   . . . where        is_<any_data_type>(<path_to_semi-structured_data_type_field>)    -   . . . where <semi-structured_data_type_column>is null    -   . . . where <semi-structured_data_type_field>is not null

Extending the pruning index to support such semi-structured predicatetypes can present a number of challenges. For example, semi-structureddata type schemas such as JSON schemas can be highly nested (e.g., afield can contain an ARRAY object, which in turn holds values ofheterogeneous types, including other complex types such as OBJECT orARRAY). As another example, semi-structured data can evolve in time(e.g., new fields can be added or existing fields can be removed). Asanother example, the data type for the same field in one row can bedifferent from the one in another row (e.g., an ID field can berepresented as a NUMBER and STRING in different rows). As yet anotherexample of the challenges posed by semi-structured data types, a singlevalue might correspond to multiple data types (e.g., a STRING value cancontain a valid DATE, TIME, TIMESTAMP, NUMBER, etc. data types). Instill another example, the same value might match against severalsemi-structured data types due to the presence of a cast function (e.g.,a TIMESTAMP value can be stored inside semi-structured data object ofany TIMESTAMP version, as a NUMBER, as a STRING of TIMESTAMP, as aSTRING of INTEGER).

To extend the pruning index to support predicates on semi-structureddata fields while addressing the foregoing challenges, operations 1005,1010, 1015, 1020, and 1025 can be performed as part of the method 800,as shown in FIG. 10 . Consistent with these embodiments, the operation1005 may be performed prior to operation 810 where the compute servicemanager 108 generates the pruning index for the source table.

At operation 1005, the compute service manager 108 generates one or moreindexing transformations for each object in a semi-structured data typecolumn of the source table. Importantly, semi-structured data types areautomatically parsed to identify all paths that can be indexed, ratherthan requiring the user to specify the path(s) to be indexed. Thecompute service manager 108 can generate an indexing transformation fora given object using a SQL cast function. Invocation of a cast functionon an object is also referred to herein as “casting”. The computeservice manager 108 uses the cast function to convert the object to astored data type. That is, the compute service manager 108 can cast theobject from an input object type to a stored data type to generate anindexing transformation. In some instances, the compute service manager108 generates an indexing transformation by casting the object from afirst logical data type (e.g., FIXED) to a second logical data type(e.g., REAL). In some instances, the compute service manager 108generates an indexing transformation by casting the object to the samelogical data type with a different scale and/or precision (e.g., aFIXED->FIXED (PRECISION, SCALE) transformation).

In instances of ARRAY and OBJECT data types, the compute service manager108 generates an indexing transformation based on a path (e.g., an SQLpath) of the data. More specifically, the compute service manager 108generates a token for the indexing transformation that indicates that acomplex path (corresponding to an ARRAY or OBJECT data type) is notindexed specifically. In an example of the forgoing, input dataincludes:

-   -   {“id”: 45, “name”: “John Appleseed”, “age”: 45}        and a received query predicate includes:    -   src:id=45        In this example, if the path (i.e., “/id/” or “/age/”) is not        used when indexing and matching, the same values will be treated        in the same way and will result in the same hashes. This can be        problematic in example instances in which there are        sender-receiving IP addresses or the same numeric values in        multiple fields. Even if the “id” was different from 45, a        pruning index look-up would still identify “45” because it is        present in the “age” field. To address the challenges        illustrated by this example, a token is generated based on a        full absolute path of the data, as mentioned above.

Table 1, presented below, lists example indexing transformations thatcan be generated for multiple input object data types.

TABLE 1 Input data type Indexing transformation FIXED FIXED → REAL FIXED→ FIXED (PRECISION, SCALE) TEXT REAL REAL REAL → FIXED TEXT TEXT TEXTTEXT → NUMBER (PRECISION, SCALE) DATE TIME TIMESTAMP DATE DATE TEXT TIMETIME TEXT TIMESTAMP_NTZ TIMESTAMP_NTZ TIMESTAMP_LTZ TEXT TIMESTAMP_TZBOOLEAN FIXED TEXT NULL_VALUE NULL_VALUE ARRAY PATH OBJECT PATH

With specific reference to FIXED and REAL data types, after parsingnumber input, values can be stored as fixed point (LogicalType::FIXED)or real (LogicalType::REAL) objects. As shown in Table 1, for FIXEDinput data types, the compute service manager 108 applies a FIXED toREAL transformation. The output value of REAL data type is stabilizedand indexed. Additionally, a FIXED to FIXED (precision, scale)transformation is performed, in which the output FIXED data type has adifferent precision or scale (e.g., 0) than the input. Although this mayreduce precision, this enables matching against all valid NUMBER(precision, scale) casts. A FIXED to TEXT transformation is alsoperformed to enable string matching. For REAL input object data types,the REAL value is stabilized and indexed if it is in the range of FIXEDdata type. In instances in which the value is out-of-range (e.g.,1e+50), the value may be discarded from indexing. A REAL to FIXEDtransformation is also performed and out-of-range REAL values arediscarded. As with FIXED data types, a REAL to TEXT transformation isperformed to enable exact string matching.

With reference to TEXT data types, textual data is indexed as text forexact string matching. Other data types such as DATE, TIME, andTIMESTAMP can be stored as TEXT objects. Thus, in order to allowpredicates on these data types, the compute service manager 108 mayattempt casting textual data to each of these data types and keepsuccessful conversions as indexing transformations.

Consistent with some embodiments, the network-based database system 102can store DATA, TIME, and TIMESTAMP data types in TEXT objects. Theseobject types can, however, be present in semi-structured data typecolumns of tables coming from external scans. When converting validtimestamp strings (and objects) into:

-   -   TIMESTAMP_NTZ=>The output will not contain a timezone. Even if        the converted string has its own timezone, it is discarded.    -   TIMESTAMP_LTZ=>The output will have a local timezone attached.        If the converted string does not have a timezone, the compute        service manager 108 may add the local timezone. If the string        already has a timezone, the compute service manager 108 may        first apply the existing timezone, then attach to the local        timezone.    -   TIMESTAMP_TZ=>There is a source local timezone but it is not        used during computations. If the converted string does not have        a timezone, the compute service manager 108 may add the local        timezone. If the string already has a timezone, that timezone is        used.

Assume STRING=DATE+[TIME]+[TZ] where current local timezone is LTZ.Then:

-   -   STRING→TIMESTAMP_NTZ=>DATE+[TIME]    -   STRING→TIMESTAMP_TZ=>DATE+[TIME]+(TZ=∅? LTZ: TZ)    -   STRING→TIMESTAMP_LTZ=>DATE+[TZ=∅? TIME: TIME+TZ−LTZ]+LTZ        TABLES 2 and 3 presented below provide examples of the forgoing        formula as applied to GMT-08:00 pacific time.

TABLE 2 STRING object without timezone information ‘2021-01-01 Fri, 01Jan 2021 23:00:00 + 0000 23:00:00’::variant::timestamp_ntz; ‘2021-01-01Fri, 01 Jan 2021 23:00:00 − 0800 23:00:00’::variant::timestamp_tz;‘2021-01-01 Fri, 01 Jan 2021 23:00:00 − 080023:00:00’::variant::timestamp_ltz;

TABLE 3 STRING object with timezone information ‘2021-01-01 Fri, 01 Jan2021 23:00:00 − 1200’::variant::timestamp_ntz; 23:00:00 + 0000‘2021-01-01 Fri, 01 Jan 2021 23:00:00 − 1200’::variant::timestamp_tz;23:00:00 − 1200 ‘2021-01-01 Sat, 02 Jan 2021 23:00:00 −1200’::variant::timestamp_ltz; 03:00:00 − 0800

Attempting to cast a STRING into all TIMESTAMP types can be very costly.Therefore, it can be more efficient to cast into only one type andgather hashes from that type. For example, it can be more efficient tocast a STRING into TIMESTAMP_TZ type since there are valid STRINGs thatare convertible to TIMESTAMP_TZ, but not any other TIMESTAMP type. Ifthe indexed STRING has its own time zone information (e.g., “1970-01-0103:25:45.000000000Ztz=1440”), casting this STRING into DATE,TIMESTAMP_NTZ or TIMESTAMP_LTZ will fail, but the cast to TIMESTAMP_TZwill succeed. This approach can be advantageous because it does notcarry any risk of missing potential successful casts from TEXT toTIMESTAMP types.

As noted by TABLE 1, indexing transformations for BOOLEAN data typescorrespond to FIXED and TEXT data types. For the BOOLEAN to FIXEDtransformation, the only possible values are ‘0’ and ‘1’. For theBOOLEAN to TEXT transformation, the only possible values are “true” and“false.”

With returned reference to FIG. 10 , the operation 1010 can be performedas part of the operation 810 where the compute service manager 108generates the pruning index. At operation 1010, the compute servicemanager 108 generates a set of fingerprints for each data object in thecolumn based on the corresponding indexing transformation(s) generatedfor the data object. That is, the compute service manager 108 generatesa set of fingerprints for a given object based on the one or moreindexing transformations generated for the object. As noted above inreference to operation 905, the set of fingerprints generated for eachobject in the column are used to generate a filter in the pruning indexthat corresponds to the column.

The compute service manager 108 can, in some instances, generate afingerprint for a given object by computing a hash over an indexingtransformation of the object or over the object itself. In other words,the set of fingerprints generated for a given object can include one ormore fingerprints generated by computing a hash over an indexingtransformation and a fingerprint generated by computing a hash over theobject itself.

As discussed above, for complex data types such as ARRAY and OBJECT, theindexing transformation corresponds to a token that indicates the path(corresponding to an ARRAY or OBJECT data type) is not specificallyindexed. In generating a fingerprint for such complex data types, thecompute service manager 108 may compute a first hash over the path, andcompute a second hash over a token using the first hash as a seed toproduce the fingerprint for the data. In some example embodiments, thehash function xxHash( ) is used to compute the hashes, though it shallbe appreciated that any one of many known hashing techniques andfunctions can be used. In a first example, the compute service manager108 can generate a fingerprint for any data type within asemi-structured data object as follows:

-   -   XxHash(<constant>, <seed>=<hash_of_the_path>)

In a second example, the compute service manager 108 can generate afingerprint for a complex data type as follows:

-   -   XxHash(XxHash(<constant>, <hash_of_the_path>), PRIME_NUMBER)

In a second example, the compute service manager 108 can generate afingerprint for a complex data type as follows:

-   -   XxHash(XxHashCombine(<constant>, <seed>=PRIME_NUMBER,    -   <intermediate>=<hash_of_the_path>), PRIME_NUMBER)

As shown, the operations 1015 and 1020 can, in some embodiments, beperformed subsequent to the operation 815 where the query directed tothe source table is received. Consistent with these embodiments, thequery can include a predicate on a semi-structured data type column. Atoperation 1015, the compute service manager 108 generates one or moreindexing transformations based on the query predicate. Similar to theindexing transformations generated for the objects in thesemi-structured column, the compute service manager 108 can generate anindexing transformation for the query predicate by executing a castfunction over one or more values in the predicate. That is, the computeservice manager 108 can use the cast function to convert a value in thequery predicate from a first data type to a second data type or to thesame data type, but with a different precision and/or scale. In someinstances, the value itself can be used as an indexing transformationwithout casting the value to a different data type.

For predicates such as IS_NOT_NULL(<semi-structured_data_type_field>)the argument semi-structured data field can correspond to both internaland leaf nodes, meaning that there is no information about the existenceof the path. Thus, the compute service manager 108 cannot simply inferwhether this path in fact contains a primitive value or represents anOBJECT or ARRAY data type. Therefore, the compute service manager 108creates an IN predicate as follows:

-   -   (<semi-structured_data_type_field>indexed as LEAF node)        Or    -   (<semi-structured_data_type_field>indexed as INTERNAL node)        Accordingly, the compute service manager 108 generates two        constants—one for the leaf path and one for the internal path        hash. These final constants can be fed into the IN predicate.

To address IN predicates in the following form:<semi-structured_data_type_field> in (C1, C2, . . . , Cn), thesemi-structured data type field can be interpreted without any Cast( )functions when the constants C1, C2, Cn are numbers. Otherwise, thecompute service manager 108 can unwrap the Cast for each constantseparately.

If the constant to match against is a STRING data type, two constantsare created. More specifically, a first constant corresponds to theconstant itself without any transformations, and a second constantcorresponds to a token that indicates that the input might represent anARRAY or an OBJECT. In an example, a query predicate includes “ . . .where name=‘[“John”]’;”. In this example, the square bracket can eitherbe part of the input string or can present an ARRAY. Hence, bothsituations are accounted for in the approach described above. In ageneral case where there are no bracket symbols present in the inputstring, only the first constant is created.

At operation 1020, the compute service manager 108 generates a set ofsearch fingerprints based on the one or more indexing transformations.As with the fingerprints generated for the searchable values in thesemi-structured column, the compute service manager 108 generates afingerprint for the query predicate by computing a hash over an indexingtransformation generated for the query predicate.

As shown, the operation 1025 can be performed as part of the operation825 where the compute service manager 108 prunes the scan set. Atoperation 1025, the compute service manager 108 identifies a subset ofpartitions to scan based on the pruning index and the searchfingerprints. The compute service manager 108 can identify the subset bycomparing the set of search fingerprints to values included in thepruning index (e.g., fingerprints of indexing transformations of storeddata values in the source table), and identifying one or more values inthe pruning index that match one or more search fingerprints.Specifically, the compute service manager 108 identifies one or moremicro-partitions that potentially store data that satisfies the querybased on fingerprints in the pruning index that match searchfingerprint(s). That is, a fingerprint (e.g., hash value computed basedon an indexing transformations of semi-structured data value) in thepruning index that matches a search fingerprint generated from anindexing transformation of the query predicate (e.g., a hash valuecomputed based on the indexing transformation) indicates that matchingdata is potentially stored in a corresponding column of themicro-partition because the indexing transformation generated from thequery predicate is stored in the column of the micro-partition. Thecorresponding micro-partition can be identified by the compute servicemanager 108 based on the matching fingerprint in the pruning index.

As shown in FIG. 11 , the operation 1005 of method 800 may, in someembodiments, include (e.g., as sub-operations or a sub-routine)operations 1105, 1110, and 1115. At operation 1105, the compute servicemanager 108 tries to cast an object in a semi-structured data typecolumn to a stored data type. That is, the compute service manager 108attempts to convert the object to the stored data type using a SQL castfunction. The object can be the first object in the column processed bythe compute service manager 108.

If the cast fails, the compute service manager 108 stores an indicatorto indicate that objects in the column cannot be cast to that particulardata type. That is, an indicator is stored to indicate that the objectsin the column are unable to be converted to the data type in response toa failed attempt to convert the object to the data type. In an example,the compute service manager 108 can insert a token in the pruning indexthat indicates that objects in the column cannot be cast to a particulardata type. As the compute service manager 108 traverses additionalobjects in the column in generating a filter for the column in thepruning index, the stored token causes the compute service manager 108to avoid further attempts at casting objects in the column to the datatype for which the casting failed. If the cast is successful, thecompute service manager 108 saves a result of the cast as an indexingtransformation for the object and a fingerprint may subsequently begenerated based on the indexing transformation, as described above. Thecompute service manager 108 casts the remaining objects in the column tothe data types for which the cast is successful.

Although only a single data type is addressed above, it shall beappreciated that this process can be repeated for each supported datatype. That is, the compute service manager 108 can try to cast theobject in the column to each of multiple different supported data types.In this manner, the compute service manager 108 can learn which datatypes objects in the column can be cast to based on which data types thefirst object in the column can be cast to, and the compute servicemanager 108 can avoid attempting to cast the remaining objects in thecolumn to data types that they cannot be cast to.

As shown in FIG. 12 , the method 800 may, in some embodiments, includeoperations 1205, 1210, 1215, 1220, and 1225. Consistent with theseembodiments, the operations 1205 and 1210 may be performed prior tooperation 810 where the compute service manager 108 generates thepruning index for the source table. At operation 1205, the computeservice manager 108 preprocesses the data values in the cells of thesource table. In preprocessing a given data value, the compute servicemanager 108 generates one or more preprocessed variants of the datavalue. In performing the preprocessing, the compute service managerperforms one or more normalization operations to a given data value. Thecompute service manager 108 can utilize one of several knownnormalization techniques to normalize data values.

For a given data value, the preprocessing performed by the computeservice manager 108 can include, for example, any one or more of:generating a case-agnostic variant (e.g., by converting uppercasecharacters to lowercase characters), generating one or more misspelledvariants based on common or acceptable misspellings of the data value,and generating one or more synonymous variants corresponding to synonymsof the data value. In general, in generating a preprocessed variant(e.g., case-agnostic variant, misspelled variant, a synonymous variantor a variant with special characters to indicate a start and end to adata value), the compute service manager 108 uses a common knowledgebase to transform a data value into one or more permutations of theoriginal data value.

As an example of the foregoing, the string “Bob” can be transformed intothe case-agnostic variant “bob.” As another example, the preprocessedvariants of “bob” “bbo” and “obb” can be generated for the string “Bob”to account for misspellings.

At operation 1210, the compute service manager 108 generates a set ofN-grams for each preprocessed variant. An N-gram in this context refersto a contiguous sequence of N-items (e.g., characters or words) in agiven value. For a given preprocessed variant of a data value in thesource table, the compute service manager 108 transforms the value intomultiple segments of equal length. For example, for a string, thecompute service manager 108 can transform the string into multiplesub-strings of N characters.

Depending on the embodiment, the value of N can be predetermined ordynamically computed at the time of generating the pruning index. Inembodiments in which the value of N is precomputed, the compute servicemanager 108 determines an optimal value for N based on a data type ofvalues in the source table. In some embodiments, multiple values of Ncan be used. That is, a first subset of N-grams can be generated using afirst value for N and a second subset of N-grams can be created using asecond value of N.

Consistent with these embodiments, the operations 1215 and 1220 can beperformed prior to operation 820 where the compute service manager 108prunes the scan set using the pruning index. At operation 1215, thecompute service manager 108 preprocesses a search pattern included inthe query. In preprocessing the search pattern, the compute servicemanager 108 performs the same preprocessing operations that areperformed on the data values in the source table at 1205 to ensure thatthe characters of the search pattern fit the pruning index. Hence, inpreprocessing the search pattern, the compute service manager 108 canperform any one or more of: generating a case-agnostic variant of thesearch pattern (e.g., by converting uppercase characters to lowercasecharacters), generating one or more misspelled variants based on commonor acceptable misspellings of the search pattern, generating one or moresynonymous variants corresponding to synonyms of the search pattern, andgenerating a variant that includes special characters to mark a startand end of the search pattern. In preprocessing a given pattern, thecompute service manager 108 can generate one or more preprocessedvariants of the search pattern. For example, the compute service manager108 can generate any one or more of: a case-agnostic variant, misspelledvariant, or a synonymous variant for the search pattern. As a furtherexample, the compute service manager 108 can generate a variant thatincludes special characters to indicate a start and end of a searchpattern (e.g., “{circumflex over ( )}testvalue$” for the search pattern“testvalue”).

At operation 1220, the compute service manager 108 generates a set ofN-grams for the search pattern based on the one or more preprocessedvariants of the search pattern. The compute service manager 108 uses thesame value for N that was used to generate the pruning index. Inembodiments in which the compute service manager 108 uses multiplevalues for N in generating the pruning index, the compute servicemanager 108 uses the same values for generating the set of N-grams forthe search pattern.

In an example, the query includes the following statement:

WHERE a ILIKE ‘%LoremIpsum%Dolor%Sit%Amet’

In this example, ‘%LoremIpsum%Dolor%Sit%Amet’ is the search pattern andin preprocessing the search pattern, the compute service manager 108converts the search pattern to all lower case to create a case-agnosticvariant: ‘%loremipsum%dolor%sit%amet’. The compute service manager 108splits the search pattern into segments at the wild card positions,which, in this example, produces the following sub-strings:“loremipsum”, “dolor”, “sit”, and “amet”. Based on these sub-strings,the compute service manager 108 generates the following set of N-grams:

Set [“lorem”, “oremi”, “remip”, “emips”, “mipsu”, “ipsum”, “dolor”]

In this example N is 5, and thus the compute service manager 108discards the sub-strings “sit” and “amet” as their length is less than5.

As shown, consistent with these embodiments, the operation 1225 can beperformed as part of the operation 825 where the compute service manager108 prunes the scan set using the pruning index. At operation 1225, thecompute service manager 108 uses the set of N-grams generated based onthe search pattern to identify a subset of micro-partitions of thesource table to scan based on the pruning index. The compute servicemanager 108 may identify the subset of micro-partitions by generating aset of fingerprints based on the set of N-grams (e.g., by computing ahash for each N-gram), comparing the set of fingerprints to valuesincluded in the pruning index (e.g., fingerprints of stored data valuesin the source table), and identifying one or more values in the pruningindex that match one or more fingerprints in the set of fingerprintsgenerated based on the N-grams of the search pattern. Specifically, thecompute service manager 108 identifies one or more micro-partitions thatpotentially store data that satisfies the query based on fingerprints ofdata values in the pruning index that match fingerprints in the set offingerprints computed for the search pattern. That is, a fingerprint(e.g., hash value computed based on an N-gram of a preprocessed storeddata value in the source table) in the pruning index that matches afingerprint generated from an N-gram of the search pattern (e.g., a hashvalue computed based on the N-gram) indicates that matching data ispotentially stored in a corresponding column of the micro-partitionbecause the N-gram generated from the search pattern is stored in thecolumn of the micro-partition. The corresponding micro-partition can beidentified by the compute service manager 108 based on the matchingfingerprint in the pruning index. Consistent with some embodiments, inidentifying the subset of micro-partitions, the compute service manager108 uses the pruning index to identify any micro-partitions that containany one of the fingerprints generated from the search pattern N-grams,and from these micro-partitions, the compute service manager 108 thenidentifies the micro-partitions that contain all of the N-grams. Thatis, the compute service manager 108 uses the pruning index to identify asubset of micro-partitions that contain data matching all fingerprintsgenerated based on the N-grams of the search pattern. For example, givenfingerprints f1, f2, and f3, the compute service manager 108 uses thepruning index to determine: a first micro-partition and secondmicro-partition contain data corresponding to f1; the secondmicro-partition and a third micro-partition that contains datacorresponding to f2; and the first, second, and third micro-partitioncontain data corresponding to f3. In this example, the compute servicemanager 108 selects only the second micro-partition for scanning basedon the second micro-partition containing data that corresponds to allthree fingerprints.

Described implementations of the subject matter can include one or morefeatures, alone or in combination as illustrated below by way ofexample.

Example 1 is a database system comprising: at least one hardwareprocessor; and at least one memory storing instructions that cause theat least one hardware processor to perform operations comprising:accessing a source table organized into a set of batch units, the sourcetable comprising a column of data corresponding to a semi-structureddata type; generating one or more indexing transformations for an objectin the column, the generating of the one or more indexing transformationcomprising converting the object to one or more stored data types;generating a pruning index for the source table based in part on the oneor more indexing transformations for the object, the pruning indexcomprising a set of filters that index distinct values in each column ofthe source table, each filter in the set of filters corresponding to abatch unit in the set of batch units; and storing, in a database, thepruning index with an association with the source table.

Example 2 includes the system of Example 1, wherein: the operationsfurther comprise generating a set of fingerprints for the object in thecolumn based on the one or more indexing transformations generated forthe object, and the generating of the pruning index comprises populatinga filter in the set of filters with the set of fingerprints.

Example 3 includes the system of any one or more of Examples 1 or 2,wherein the generating of the set of fingerprints for the objectcomprise generating a fingerprint for the object by computing a hashbased on an indexing transformation for the object.

Example 4 includes the system of any one or more of Examples 1-3,wherein the converting of the object to one or more stored data typescomprising executing a cast function on the object.

Example 5 includes the system of any one or more of Examples 1-4,wherein generating the one or more indexing transformations comprises:attempting to convert the object to a stored data type; and in responseto a failed attempt to convert the object, storing an indicator thatobjects in the column are unable to be converted to the stored datatype.

Example 6 includes the system of any one or more of Examples 1-5,wherein generating the one or more indexing transformations comprises:attempting to convert the object to a stored data type; and in responseto a successful attempt, saving a result as an indexing transformationfor the object.

Example 7 includes the system of any one or more of Examples 1-6,wherein the generating of the one or more indexing transformationscomprises: determining a path corresponding to the object.

Example 8 includes the system of any one or more of Examples 1-7,wherein the operations further comprise: receiving a query including apredicate directed at the column corresponding to the semi-structureddata type; generating one or more indexing transformations based on avalue in the predicate; generating a set of search fingerprints based onthe one or more indexing transformations; pruning the set of batch unitsto scan for data matching the predicate using the pruning index and theset of search fingerprints; and processing the query by scanning asubset of batch units resulting from pruning the set of batch units.

Example 9 includes the system of any one or more of Examples 1-8,wherein the pruning of the set of batch units comprises: comparing theset of search fingerprints to the pruning index; and identifying one ormore values in the pruning index that match at least one searchfingerprint in the set of search fingerprints.

Example 10 includes the system of any one or more of Examples 1-9,wherein the pruning of the set of batch units comprises: identifying asubset of batch units to scan for matching data based on the one or morevalues in the pruning index that match at least one search fingerprintin the set of search fingerprints.

Example 11 is a method comprising: accessing a source table organizedinto a set of batch units, the source table comprising a column of datacorresponding to a semi-structured data type; generating one or moreindexing transformations for an object in the column, the generating ofthe one or more indexing transformation comprising converting the objectto one or more stored data types; generating a pruning index for thesource table based in part on the one or more indexing transformationsfor the object, the pruning index comprising a set of filters that indexdistinct values in each column of the source table, each filter in theset of filters corresponding to a batch unit in the set of batch units;and storing, in a database, the pruning index with an association withthe source table.

Example 12 includes the method of Example 11, and further comprises:generating a set of fingerprints for the object in the column based onthe one or more indexing transformations generated for the object,wherein the generating of the pruning index comprises populating afilter in the set of filters with the set of fingerprints.

Example 13 includes the method of any one or more of Examples 11 or 12,wherein the generating of the set of fingerprints for the objectcomprise generating a fingerprint for the object by computing a hashbased on an indexing transformation for the object.

Example 14 includes the method of any one or more of Examples 11-13,wherein the converting of the object to one or more stored data typescomprising executing a cast function on the object.

Example 15 includes the method of any one or more of Examples 11-14,wherein generating the one or more indexing transformations comprises:attempting to convert the object to a stored data type; and in responseto a failed attempt to convert the object, storing an indicator thatobjects in the column are unable to be converted to the stored datatype.

Example 16 includes the method of any one or more of Examples 11-15,wherein generating the one or more indexing transformations comprises:attempting to convert the object to a stored data type; and in responseto a successful attempt, saving a result as an indexing transformationfor the object.

Example 17 includes the method of any one or more of Examples 11-16,wherein the generating of the one or more indexing transformationscomprises: determining a path corresponding to the object.

Example 18 includes the method of any one or more of Examples 11-17,further comprising: receiving a query including a predicate directed atthe column corresponding to the semi-structured data type; generatingone or more indexing transformations based on a value in the predicate;generating a set of search fingerprints based on the one or moreindexing transformations; pruning the set of batch units to scan fordata matching the predicate using the pruning index and the set ofsearch fingerprints; and processing the query by scanning a subset ofbatch units resulting from pruning the set of batch units

Example 19 includes the method of any one or more of Examples 11-18,wherein the pruning of the set of batch units comprises: comparing theset of search fingerprints to the pruning index; and identifying one ormore values in the pruning index that match at least one searchfingerprint in the set of search fingerprints.

Example 20 includes the method of any one or more of Examples 11-19,wherein the pruning of the set of batch units comprises: identifying asubset of batch units to scan for matching data based on the one or morevalues in the pruning index that match at least one search fingerprintin the set of search fingerprints.

Example 21 is a computer-storage medium storing instructions that causeat least one hardware processor to perform operations comprising:accessing a source table organized into a set of batch units, the sourcetable comprising a column of data corresponding to a semi-structureddata type; generating one or more indexing transformations for an objectin the column, the generating of the one or more indexing transformationcomprising converting the object to one or more stored data types;generating a pruning index for the source table based in part on the oneor more indexing transformations for the object, the pruning indexcomprising a set of filters that index distinct values in each column ofthe source table, each filter in the set of filters corresponding to abatch unit in the set of batch units; and storing, in a database, thepruning index with an association with the source table.

Example 22 includes the computer-storage medium of Example 21, wherein:the operations further comprise generating a set of fingerprints for theobject in the column based on the one or more indexing transformationsgenerated for the object, and the generating of the pruning indexcomprising populating a filter in the set of filters with a set offingerprints generated based on the one or more indexing transformationfor the object.

Example 23 includes the computer-storage medium of any one or more ofExamples 21 or 22, wherein the generating of the set of fingerprints forthe object comprise generating a fingerprint for the object by computinga hash based on an indexing transformation for the object.

Example 24 includes the computer-storage medium of any one or more ofExamples 21-23, wherein the converting of the object to one or morestored data types comprising executing a cast function on the object.

Example 25 includes the computer-storage medium of any one or more ofExamples 21-24, wherein generating the one or more indexingtransformations comprises: attempting to convert the object to a storeddata type; and in response to a failed attempt to convert the object,storing an indicator that objects in the column are unable to beconverted to the stored data type.

Example 26 includes the computer-storage medium of any one or more ofExamples 21-25, wherein generating the one or more indexingtransformations comprises: attempting to convert the object to a storeddata type; and in response to a successful attempt, saving a result asan indexing transformation for the object.

Example 27 includes the computer-storage medium of any one or more ofExamples 21-26, wherein the generating of the one or more indexingtransformations comprises: determining a path corresponding to theobject.

Example 28 includes the computer-storage medium of any one or more ofExamples 21-27, wherein the operations further comprise: receiving aquery including a predicate directed at the column corresponding to thesemi-structured data type; generating one or more indexingtransformations based on a value in the predicate; generating a set ofsearch fingerprints based on the one or more indexing transformations;pruning the set of batch units to scan for data matching the predicateusing the pruning index and the set of search fingerprints; andprocessing the query by scanning a subset of batch units resulting frompruning the set of batch units.

Example 29 includes the computer-storage medium of any one or more ofExamples 21-28, wherein the pruning of the set of batch units comprises:comparing the set of search fingerprints to the pruning index; andidentifying one or more values in the pruning index that match at leastone search fingerprint in the set of search fingerprints.

Example 30 includes the computer-storage medium of any one or more ofExamples 21-29, wherein the pruning of the set of batch units comprises:identifying a subset of batch units to scan for matching data based onthe one or more values in the pruning index that match at least onesearch fingerprint in the set of search fingerprints.

FIG. 13 illustrates a diagrammatic representation of a machine 1300 inthe form of a computer system within which a set of instructions may beexecuted for causing the machine 1300 to perform any one or more of themethodologies discussed herein, according to an example embodiment.Specifically, FIG. 13 shows a diagrammatic representation of the machine1300 in the example form of a computer system, within which instructions1316 (e.g., software, a program, an application, an applet, an app, orother executable code) for causing the machine 1300 to perform any oneor more of the methodologies discussed herein may be executed. Forexample, the instructions 1316 may cause the machine 1300 to execute anyone or more operations of any one or more of the method 800. As anotherexample, the instructions 1316 may cause the machine 1300 to implementportions of the functionality illustrated in any one or more of FIGS.4-8 . In this way, the instructions 1316 transform a general,non-programmed machine into a particular machine 1300 (e.g., the computeservice manager 108, the execution platform 110, and the data storagedevices 206) that is specially configured to carry out any one of thedescribed and illustrated functions in the manner described herein.

In alternative embodiments, the machine 1300 operates as a standalonedevice or may be coupled (e.g., networked) to other machines. In anetworked deployment, the machine 1300 may operate in the capacity of aserver machine or a client machine in a server-client networkenvironment, or as a peer machine in a peer-to-peer (or distributed)network environment. The machine 1300 may comprise, but not be limitedto, a server computer, a client computer, a personal computer (PC), atablet computer, a laptop computer, a netbook, a smart phone, a mobiledevice, a network router, a network switch, a network bridge, or anymachine capable of executing the instructions 1316, sequentially orotherwise, that specify actions to be taken by the machine 1300.Further, while only a single machine 1300 is illustrated, the term“machine” shall also be taken to include a collection of machines 1300that individually or jointly execute the instructions 1316 to performany one or more of the methodologies discussed herein.

The machine 1300 includes processors 1310, memory 1330, and input/output(I/O) components 1350 configured to communicate with each other such asvia a bus 1302. In an example embodiment, the processors 1310 (e.g., acentral processing unit (CPU), a reduced instruction set computing(RISC) processor, a complex instruction set computing (CISC) processor,a graphics processing unit (GPU), a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a radio-frequencyintegrated circuit (RFIC), another processor, or any suitablecombination thereof) may include, for example, a processor 1312 and aprocessor 1314 that may execute the instructions 1316. The term“processor” is intended to include multi-core processors 1310 that maycomprise two or more independent processors (sometimes referred to as“cores”) that may execute instructions 1316 contemporaneously. AlthoughFIG. 13 shows multiple processors 1310, the machine 1300 may include asingle processor with a single core, a single processor with multiplecores (e.g., a multi-core processor), multiple processors with a singlecore, multiple processors with multiple cores, or any combinationthereof.

The memory 1330 may include a main memory 1332, a static memory 1334,and a storage unit 1336, all accessible to the processors 1310 such asvia the bus 1302. The main memory 1332, the static memory 1334, and thestorage unit 1336 store the instructions 1316 embodying any one or moreof the methodologies or functions described herein. The instructions1316 may also reside, completely or partially, within the main memory1332, within the static memory 1334, within the storage unit 1336,within at least one of the processors 1310 (e.g., within the processor'scache memory), or any suitable combination thereof, during executionthereof by the machine 1300.

The I/O components 1350 include components to receive input, provideoutput, produce output, transmit information, exchange information,capture measurements, and so on. The specific I/O components 1350 thatare included in a particular machine 1300 will depend on the type ofmachine. For example, portable machines such as mobile phones willlikely include a touch input device or other such input mechanisms,while a headless server machine will likely not include such a touchinput device. It will be appreciated that the I/O components 1350 mayinclude many other components that are not shown in FIG. 13 . The I/Ocomponents 1350 are grouped according to functionality merely forsimplifying the following discussion and the grouping is in no waylimiting. In various example embodiments, the I/O components 1350 mayinclude output components 1352 and input components 1354. The outputcomponents 1352 may include visual components (e.g., a display such as aplasma display panel (PDP), a light emitting diode (LED) display, aliquid crystal display (LCD), a projector, or a cathode ray tube (CRT)),acoustic components (e.g., speakers), other signal generators, and soforth. The input components 1354 may include alphanumeric inputcomponents (e.g., a keyboard, a touch screen configured to receivealphanumeric input, a photo-optical keyboard, or other alphanumericinput components), point-based input components (e.g., a mouse, atouchpad, a trackball, a joystick, a motion sensor, or another pointinginstrument), tactile input components (e.g., a physical button, a touchscreen that provides location and/or force of touches or touch gestures,or other tactile input components), audio input components (e.g., amicrophone), and the like.

Communication may be implemented using a wide variety of technologies.The I/O components 1350 may include communication components 1364operable to couple the machine 1300 to a network 1380 or devices 1370via a coupling 1382 and a coupling 1372, respectively. For example, thecommunication components 1364 may include a network interface componentor another suitable device to interface with the network 1380. Infurther examples, the communication components 1364 may include wiredcommunication components, wireless communication components, cellularcommunication components, and other communication components to providecommunication via other modalities. The devices 1370 may be anothermachine or any of a wide variety of peripheral devices (e.g., aperipheral device coupled via a universal serial bus (USB)). Forexample, as noted above, the machine 1300 may correspond to any one ofthe compute service manager 108, the execution platform 110, and thedevices 1370 may include the data storage device 206 or any othercomputing device described herein as being in communication with thenetwork-based data warehouse system 102 or the storage platform 104.

The various memories (e.g., 1330, 1332, 1334, and/or memory of theprocessor(s) 1310 and/or the storage unit 1336) may store one or moresets of instructions 1316 and data structures (e.g., software) embodyingor utilized by any one or more of the methodologies or functionsdescribed herein. These instructions 1316, when executed by theprocessor(s) 1310, cause various operations to implement the disclosedembodiments.

As used herein, the terms “machine-storage medium,” “device-storagemedium,” and “computer-storage medium” mean the same thing and may beused interchangeably in this disclosure. The terms refer to a single ormultiple storage devices and/or media (e.g., a centralized ordistributed database, and/or associated caches and servers) that storeexecutable instructions and/or data. The terms shall accordingly betaken to include, but not be limited to, solid-state memories, andoptical and magnetic media, including memory internal or external toprocessors. Specific examples of machine-storage media, computer-storagemedia, and/or device-storage media include non-volatile memory,including by way of example semiconductor memory devices, e.g., erasableprogrammable read-only memory (EPROM), electrically erasableprogrammable read-only memory (EEPROM), field-programmable gate arrays(FPGAs), and flash memory devices; magnetic disks such as internal harddisks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROMdisks. The terms “machine-storage media,” “computer-storage media,” and“device-storage media” specifically exclude carrier waves, modulateddata signals, and other such media, at least some of which are coveredunder the term “signal medium” discussed below.

In various example embodiments, one or more portions of the network 1380may be an ad hoc network, an intranet, an extranet, a virtual privatenetwork (VPN), a local-area network (LAN), a wireless LAN (WLAN), awide-area network (WAN), a wireless WAN (WWAN), a metropolitan-areanetwork (MAN), the Internet, a portion of the Internet, a portion of thepublic switched telephone network (PSTN), a plain old telephone service(POTS) network, a cellular telephone network, a wireless network, aWi-Fi® network, another type of network, or a combination of two or moresuch networks. For example, the network 1380 or a portion of the network1380 may include a wireless or cellular network, and the coupling 1382may be a Code Division Multiple Access (CDMA) connection, a GlobalSystem for Mobile communications (GSM) connection, or another type ofcellular or wireless coupling. In this example, the coupling 1382 mayimplement any of a variety of types of data transfer technology, such asSingle Carrier Radio Transmission Technology (1×RTT), Evolution-DataOptimized (EVDO) technology, General Packet Radio Service (GPRS)technology, Enhanced Data rates for GSM Evolution (EDGE) technology,third Generation Partnership Project (3GPP) including 3G, fourthgeneration wireless (4G) networks, Universal Mobile TelecommunicationsSystem (UMTS), High-Speed Packet Access (HSPA), WorldwideInteroperability for Microwave Access (WiMAX), Long Term Evolution (LTE)standard, others defined by various standard-setting organizations,other long-range protocols, or other data transfer technology.

The instructions 1316 may be transmitted or received over the network1380 using a transmission medium via a network interface device (e.g., anetwork interface component included in the communication components1364) and utilizing any one of a number of well-known transfer protocols(e.g., hypertext transfer protocol (HTTP)). Similarly, the instructions1316 may be transmitted or received using a transmission medium via thecoupling 1372 (e.g., a peer-to-peer coupling) to the devices 1370. Theterms “transmission medium” and “signal medium” mean the same thing andmay be used interchangeably in this disclosure. The terms “transmissionmedium” and “signal medium” shall be taken to include any intangiblemedium that is capable of storing, encoding, or carrying theinstructions 1316 for execution by the machine 1300, and include digitalor analog communications signals or other intangible media to facilitatecommunication of such software. Hence, the terms “transmission medium”and “signal medium” shall be taken to include any form of modulated datasignal, carrier wave, and so forth. The term “modulated data signal”means a signal that has one or more of its characteristics set orchanged in such a manner as to encode information in the signal.

The terms “machine-readable medium,” “computer-readable medium,” and“device-readable medium” mean the same thing and may be usedinterchangeably in this disclosure. The terms are defined to includeboth machine-storage media and transmission media. Thus, the termsinclude both storage devices/media and carrier waves/modulated datasignals.

The various operations of example methods described herein may beperformed, at least partially, by one or more processors that aretemporarily configured (e.g., by software) or permanently configured toperform the relevant operations. Similarly, the methods described hereinmay be at least partially processor-implemented. For example, at leastsome of the operations of the method 800 may be performed by one or moreprocessors. The performance of certain of the operations may bedistributed among the one or more processors, not only residing within asingle machine, but also deployed across a number of machines. In someexample embodiments, the processor or processors may be located in asingle location (e.g., within a home environment, an office environment,or a server farm), while in other embodiments the processors may bedistributed across a number of locations.

Although the embodiments of the present disclosure have been describedwith reference to specific example embodiments, it will be evident thatvarious modifications and changes may be made to these embodimentswithout departing from the broader scope of the inventive subjectmatter. Accordingly, the specification and drawings are to be regardedin an illustrative rather than a restrictive sense. The accompanyingdrawings that form a part hereof show, by way of illustration, and notof limitation, specific embodiments in which the subject matter may bepracticed. The embodiments illustrated are described in sufficientdetail to enable those skilled in the art to practice the teachingsdisclosed herein. Other embodiments may be used and derived therefrom,such that structural and logical substitutions and changes may be madewithout departing from the scope of this disclosure. This DetailedDescription, therefore, is not to be taken in a limiting sense, and thescope of various embodiments is defined only by the appended claims,along with the full range of equivalents to which such claims areentitled.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This disclosure is intended to coverany and all adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent, to those of skill inthe art, upon reviewing the above description.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended; that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim is still deemed to fall within thescope of that claim.

What is claimed is:
 1. A method comprising: receiving a query includinga predicate directed at semi-structured data in a table organized into aset of batch units; generating one or more indexing transformationsbased on a value in the predicate, the generating of the one or moreindexing transformations comprising executing a cast function on thevalue in the predicate to convert the value from a first data type to asecond data type; pruning, using a pruning index, the set of batch unitsbased on the one or more indexing transformations, the pruning indexcomprising a set of filters that index distinct values in each column ofthe table; and processing the query by scanning a subset of batch unitsresulting from pruning the set of batch units.
 2. The method of claim 1,wherein generating the one or more indexing transformations based on thevalue in the predicate comprises converting the value to one or morestored data types.
 3. The method of claim 2, wherein converting thevalue comprises executing a cast function on the value.
 4. The method ofclaim 1, wherein the pruning of the set of batch units comprises:computing a hash based on an indexing transformation for the value inthe predicate; and comparing the hash to the pruning index; andidentifying one or more values in the pruning index that match the hash.5. The method of claim 4, wherein the pruning of the set of batch unitscomprises: identifying the subset of batch units to scan for matchingdata based in part on the one or more values in the pruning index thatmatch the hash.
 6. The method of claim 1, further comprising: generatingone or more indexing transformations of the semi-structured data; andgenerating the pruning index for the table based in part on one or moreindexing transformations for the semi-structured data.
 7. The method ofclaim 6, further comprising computing a hash over an indexingtransformation generated for the semi-structured data, wherein thegenerating of the pruning index comprises populating a filter in the setof filters using the hash.
 8. The method of claim 6, wherein thegenerating of the one or more indexing transformation for thesemi-structured data comprises converting a semi-structured data objectto one or more stored data types.
 9. The method of claim 8, wherein theconverting of the semi-structured data object to the one or more storeddata types comprising executing the cast function on the semi-structureddata object.
 10. The method of claim 8, wherein generating the one ormore indexing transformations comprises: attempting to convert thesemi-structured data object to a stored data type; and in response to afailed attempt to convert the semi-structured data object, storing anindicator that objects in the column are unable to be converted to thestored data type.
 11. The method of claim 8, wherein generating the oneor more indexing transformations comprises: attempting to convert thesemi-structured data object to a stored data type; and in response to asuccessful attempt, saving a result as an indexing transformation forthe semi-structured data object.
 12. A database system comprising: atleast one hardware processor; and at least one memory storinginstructions that cause the at least one hardware processor to performoperations comprising: receiving a query including a predicate directedat semi-structured data in a table organized into a set of batch units;generating one or more indexing transformations based on a value in thepredicate, the generating of the one or more indexing transformationscomprising executing a cast function on the value in the predicate toconvert the value from a first data type to a second data type; pruning,using a pruning index, the set of batch units based on the one or moreindexing transformations, the pruning index comprising a set of filtersthat index distinct values in each column of the table; and processingthe query by scanning a subset of batch units resulting from pruning theset of batch units.
 13. The database system of claim 12, whereingenerating the one or more indexing transformations based on the valuein the predicate comprises converting the value to one or more storeddata types.
 14. The database system of claim 13, wherein converting thevalue comprises executing a cast function on the value.
 15. The databasesystem of claim 12, wherein the pruning of the set of batch unitscomprises: computing a hash based on an indexing transformation for thevalue in the predicate; and comparing the hash to the pruning index; andidentifying one or more values in the pruning index that match the hash.16. The database system of claim 12, wherein the operations furthercomprise: generating one or more indexing transformations for thesemi-structured data; and generating the pruning index for the tablebased in part on one or more indexing transformations for thesemi-structured data.
 17. The database system of claim 16, wherein: theoperations further comprise computing a hash over an indexingtransformation generated for the semi-structured data, and thegenerating of the pruning index comprises populating a filter in the setof filters using the hash.
 18. The database system of claim 16, whereinthe generating of the one or more indexing transformation for thesemi-structured data comprises converting a semi-structured data objectto one or more stored data types.
 19. The database system of claim 18,wherein the converting of the semi-structured data object to the one ormore stored data types comprising executing a cast function on thesemi-structured data object.
 20. A computer-storage medium comprisinginstructions that, when executed by one or more processors of a machine,configure the machine to perform operations comprising: receiving aquery including a predicate directed at semi-structured data in a tableorganized into a set of batch units; generating one or more indexingtransformations based on a value in the predicate, the generating of theone or more indexing transformations comprising executing a castfunction on the value in the predicate to convert the value from a firstdata type to a second data type; pruning, using a pruning index, the setof batch units based on the one or more indexing transformations, thepruning index comprising a set of filters that index distinct values ineach column of the table; and processing the query by scanning a subsetof batch units resulting from pruning the set of batch units.